Flexible metal tube



Feb. 27, 1940. E wlTZENMANN 2,191,690

FLEXIBLE METAL TUBE Filed Aug. 16, 1937 //7 van tor:

Patented Feb. 27, 1940 PATENT OFFl -Cii FLEXIBLE METAL TUBE Emil Witzcnmann, Pforzheim, Baden, Germany, assignor to 0. Meyer-Keller & Co. A. G.,

Lucerne, Switzerland Application August 16, 1937, Serial No. 159,411 In Germany June 29, 1936 2 Claims.

It has already been proposed to form flexible metal tubes, especially such as are made of a helically wound metal strip of corrugated cross section, with double walls, the inner tube being welded at the joint, and the edges of the outer tube (which acts as a reinforcement for the inner tube) being interconnected without welding. for example by interbeading, interfolding or the like.

In connection with such double walled flexible metal tubes it has also been proposed to weld the outer tube at the joint and to wind the inner tube loosely, that is to say, with an open joint.

The first mentioned form of tube has the deiect that in the case of substantial wall thickness, as employed in making tubes intended to resist high pressures, the said interbeading or interfolding is very difficult if not impossible to make, and furthermore if applied to the crests of the undulations it is in the way, while in the trough of the corrugations it takes up more space than is at disposal between the adjacent projecting portions of the undulations.

in the second mentioned form, wherein the inner tube is loosely wound, the latter provides reinforcement for the welded outer tube, but the construction is unsatisfactory in some cases since there is no outer protective sheath for the welded tube, such being desirable in this special form of flexible tube. Moreover, in the last mentioned kind of double tube only an inner tube was used which was wound from a strip having one central wave crest and two lateral wave troughs- The winding thereof was diflicult on account of the width of the strip, particularly in cases where the strip material was thick and the diameter of the tube wound comparatively small. Further- ;"uore, the that the strip forming the inner tube had in cross section a central wave crest and two lateral troughs impaired the mobility of the finished tube.

The part of a composite flexible metal corrugated tube most exposed to fracture is the wave trough, so that the stresses in the wave trough are more favourable if the outer protective tube is constructed with its helical joint extending along the wave crest of the inner tube.

An object of the present invention is to provide an improved tube of this kind wherein the joint edges of the outer tube are plain and open to constitute movement limiting means, without impairing the flexibility of the tube structure, in the event of the composite tube being subjected to bending stresses, and wherein a helically wound strip smoothly overlaps the joint edges of said outer tube thereby to ensure correct operation of the said edges, as movement limiting means by preventing them overlapping, said helically wound strip also serving to prevent injury to the fingers of a person handling the tube.

The single figure of the accompanying drawing shows a fragment of a tube according to the invention, partly in section and partly in elevatron.

(1 indicates a flexible metal tube produced in known manner by helically winding a metal strip of corrugated cross section, the adjacent edges of the wound corrugated strip being welded together at a. This tube ais surrounded by an outer metal tube b also helically wound, a feature of this tube being that the strip forming it is in the form of a single wave trough with crest portions adjoining the side walls thereof and having plain edges, the crest portions of the tube Wound from this strip surrounding the crests of the welded inner tube a with the exception of a joint a extending along the helical centre line of the last mentioned crests. The joint a is covered by a helically wound strip b which smoothly overlaps the joint edges of the outer tube b.

As will be readily appreciated, when for example a high inner pressure occurs in the direction of the arrow I, this pressure will tend to expand the inner tube a and so far as this tube itself is concerned the tendency may be so pronounced that it would involve the destruction (bursting) of the walls of the tube; but owing to the fact that the outer tube b surrounds the inner tube a with the open joint a the tensional stresses applied to the tube a are limited because when undue expansion or bending of the inner tube occurs the outer tube b is also expanded or bent, but only until the adjacent joint edges of the outer tube abut. Thus, the joint edges of the outer tube constitute movement limiting means and their correct operation is ensured by the strip 1) which prevents the joint edges of the outer tube from overlapping. Furthermore, the said strip 1) constitutes a reinforcement preventing undue wear and damage of the outer tube by contact with the ground or other hard objects. Manifestly, the strip 1) may be of a harder metal than the rest of the tube structure without impairing the flexibility of the tube structure as a whole. Finally, the strip 2) overlapping the open joint of the outer tube 1) prevents the fingers of a person handling the tube from being injured by contact with the joint. In a word, the open joint is smoothly covered.

2. A flexible metal composite tube comprising I an inner tube formed of a helically wound metal strip of corrugated cross section welded at the helical joint, a conforming outer tube formed of a helically'wound open-jointed metal strip presenting in cross section a single trough with crest portions integral with its side walls and having plain edges, the plain edges of said outer tube extending along the helical centre line of the wave crests of said inner tube and'serving as movement limiting means when the composite tube is subjected to bending stresses, and a helically wound strip smoothly overlapping the joint edges of said outer tube.

EMIL WITZENMANN. 

